Flash lamp



June 27, 1933. 5,1 Ble 1,915,591

FLASH LAMP Filed May 27, 1951 In wanton Ali? Patented June 27 1933 UNITED STATES PATENT OFFICE ORRICK H. BIGGS, OF BEVERLY, 'MASSACHUSETTS, ASSIG -NOR TO GRADE SYLVAHIA' CORPORATION, OF SALEM, MLASSACHUSETTS, A CORPORATION OF MASSACHUSETTS FLASH LAMP Application filed Kay 27,

This invention relates to lamps of the type disclosed-in the patent to Ostermeier No. 1,776,637, granted September 23, 1930, comprising an evacuated transparent envelope such as an ordinary light bulb containing flashmaterial such as aluminum foil, oxygen (or oxygen-yielding material) to unite with the flash material in rapid combustion, and an .igniter for starting the combustion.

While such lamps have marked advantages over prior photo-flash devices as heretofore constructed, they have the very serious disadvantage in that about one per thousand explodes when flashed, throwing the finely broken glass many feet and constituting a grave danger to the sight of those -in the vicinity.- r

This invention involves the discovery that these explosions are due to leakage of air into the bulbs and/or to the leakage of combustible gas into the bulb from the cement used in mounting the base of the lamp on the bulb. Whereas an ordinaryincandescent lamp and the like may be tested before use by lighting the lamp, in the-case of photo-flash lamps no ractical way has as yet been found to test or accidental leakage during manufacture.

Heretofore these lamps have been manufactured with bakelite as the cement between base and bulb, using alcohol as a softener for the bakelite. In the present methods of manufacture accidental leakage is most likely to occur in this region of the bulb, and in such cases I have found that alcohol vapor passes into the bulb during the cementing process, thereby creating a condition which results in exceptionally violent explosions when the 1am is subsequently flashed.

oreover, with a pressure of oxygen approximating 120-180 mm. hg., as these lamps have heretofore been manufactured, I have found that if air alone leaks into the bulb, an explosion of more or less violence depending upon'the degree of leakage is likely to 'occur when the lamp is flashed. In general the likelihood and/or violence of explosion, with the aforesaid pressure of oxygen, increases with increased air leakage up to an air pressure approximatin that'of the oxygen (approximately onefth atmosphere) 1931. Serial 1%. 540,212.

. gases in the'air, and that the decrease in danger beyond the optimium'air pressure of approximately one-fifth atmosphere is due to reduced rate of combustion resulting from retarded diflusion of the oxygen through the nitrogen.

Various attempts have been made to mitigate thedanger of the aforesaid explosions but so far as I am aware they have not been successful. It has been proposed to increase the strength of the glass sufficiently to withstand the force of the explosive pressures: while the number of explosions may thus be reduced, those which do occur are correspondingly more violent; moreover this expedient reduces efiiciency, due to decreased transparency, and increases the cost of manufacture. It has also been proposed to coat the inside of the glass bulb with a layer of cellulosic. material such as parlodion: this not only decreases the efliciency and increases the costbut the bulbs are not as satisfactory in use.

In sharp contradistinction to these prior expedients to resist the explosive pressures,

the present invention eliminates explosions by sealing each bulb to its base in such manner as v to prevent .the passage of much if any 'combustible gas into the bulb in case of leakage in the region of the base and by altering the contents of the bulb to prevent explosion irrespective of the amount of air leakage, that is, throughout the entire range of air pressures from zero to atmospheric pressure.

For the purpose of illustration, the single figure shows, in elevation, a typical photoflash lamp comprising a bulb 1, a base 2, sealed to the bulb with intervening cement 3, flash material 4 such as aluminum foil, and an igniter 5. I

In its preferred form, this invention involves the reduction of the oxygen pressure from approximately one-fifth atmosphere to a pressure of approximately one decimeter of mercury.- This comparatively small re- .duction has the novel result of eliminating explosions due to air lealgige, even in the region of one-fifth atmosp ore of air where ficient oxygen completely to oxidize the usual the explosions occurred with greatest force 'in the prior tubes. I believe this result is due chiefly to a substantial decrease in the rate of diffusion of the oxygen through the nitrogen to the coil. owing to the decreased oxygen pressure, with a consequent reduction in the rate of combustion, resulting temperatures, and consequently of nitrogen expansion. In any event extensive tests show that this slight decrease in the oxygen pressure substantially eliminates explosions due to air leakage.

While this reduction in oxygen ressure makes the flash somewhat slower, t e same amount of light may be obtained by usin an envelope or bulb large enough to hold su amount of flash material. Indeed it is mi- 4 necessary to increase the size of the bulb beyond the present standard (approximately 200 and 250 c.c.) unless more than the usual quantity (approximately 0.090 gms), of flash material is used. a

The novel function of the aforesaid reduction in oxygen pressure may be made more apparent by contrasting it with a corresponding reductlon in the quantity of flash material: while the former reduces the speed of flashing, it does not necessitate any decrease in the total light, merely spreading the light over a longer period of time, whereas the latter would not only decrease the amount of light but it would have comparatively little tendency to avoid explosions inasmuch as it would not afiect'the rate of combustion, nor the rate of nitrogen expansion. I Referring again. to the drawing, the bulb 1 is customari y sealed to the base 2 with a cement 3 comprising bakelite softened with alcohol which of course evaporates during the setting process. In case of incipient fracture at the base-end of the bulb, where fractures are most likely to develop in the process'of sealing off the bulb, some of the alcohol vapor finds its wa into the bulb during the sealing process. T is combustible vapor renders the bulb highly explosive, especially if some air has also leaked in as would ord1 narily occur; and when the bulb is subsequently used for flash purposes it explodes with violence.

Accordin to the present invention this dan r is eliminated by employing a cement, pre erably a thermoplastic cementsuch 'as akelite, which is substantiall free from combustible vapor in the sea ing process, more articularly the. bakelite is plasticized by holding it in suspension in a non-inflammable liquid such, as glue, the preferred composition comprising:

ture is applied between bulb and base the glue breaks down and the bakelite serves as the permanent bond.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim: I

1. A flash lamp comprising a transparent envelope containing flash material and oxygen ata pressure confined to approximately one decimeter of mercury.

2. A flash lamp of the type comprising a transparent envelope containing flash material in quantity suflicient, in relation to the strengthof'the envelope, to explode the envelope by rapid combustion in the presence of air at a pressure below atmospheric, the envelope also containing oxygen, characterized in that the pressure of the oxygen is too low to explode the envelope in the presence of I 100 gm. bak elite #6040- 57% gravametric 25 gm. ground hard glue. 14% gravametric cc wate r 29% gravametric "During the 'baking process after the mix- 

